1. Field
This application relates to termination of a subsea fiber optic cable, specifically a small form-factor armored cable termination/fiber-optic seal which facilitates a connection between a subsea fiber optic cable and a pressure housing in an environment with a pressure gradient between the external environment and the pressure housing interior.
2. Description of Related Art
One of the key challenges in subsea system design is to provide a high-reliability, redundant penetration into 1-atmosphere pressure housings. This task is more difficult in subsea optical systems where a fiber optic cable must be cut to allow for interconnection within a pressure housing. The termination going into this housing should ideally seal the cable tubes and fibers to prevent leakage into the pressure housing, while maintaining the original cable break-strength.
Several related art methods exist for cable termination and tube and fiber seals, each of which have their own disadvantages.
Wedge cones, cable compression fittings, and epoxy cones may all be used to terminate various cable types. A wedge cone may be used to terminate armored cable. While wedge cones have sufficiently high strength, wedge cones and housings are specific to their cable type and are labor intensive to terminate. A cable compression fitting which grips cable may be installed with relative ease, but provides relatively lower strength. Epoxy cones—cable tubes and armor wires glued in a cone—can be applied to many cable geometries, but the epoxy used degrades over time and effectiveness is dependent on manufacturing process repeatability.
Methods for tube and fiber seals include Morrison seals, boot seals, epoxy glands, and ferrule based penetrators. Morrison seals provide bi-directional tube sealing while boot seals are limited to single direction sealing. Because Morrison seals and boot seals only block leakage around a cable tube, they are ineffective in the event of a cable tube breach and leakage with in the cable tube. Epoxy glands—wherein an epoxy seals a fiber tube to form a water tight barrier—may be applied to many cable geometries and provide seals for both tubes and fibers. The fibers and tubes are not individually isolated, however, and may allow pressurized water to leak from tube to tube. Ferrule-based penetrators—where ferrule is soldered onto fiber—provides hermetic seal, but are expensive to deploy and requires additional splices in optical system.
FIG. 4 illustrates one example of a fiber optic cable 11. Referring to FIG. 4, cable 11 may include a stainless steel central tube 54 containing one or more optical fibers 55 and one or more armor wires 52 wrapped around the central tube 54. Additional stainless steel cable tubes 53 containing one or more optical fibers 55 may be interspersed in the cable armor wire layers. Cable 11 is jacketed with a cable sheath 51 (for example, polyethylene, thermoplastic polyurethane, hytrel, etc.). While FIG. 4 illustrates one exemplary embodiment of fiber optic cable 11, one of ordinary skill in the art would recognize that fiber optic cable 11 may be realized using other configurations.